1. Field of the Invention
This present invention relates to a press die set used in a punching process, a bending process, a drawing process, a coining process, a forging process, a rubber die process, a mold die process, a die-cast process, a powder molding process or the like, and in particular to a slidable part such as a guide post, a retainer, and a guide bushing in the die set. Further, the present invention relates to a roller and a frame constituting a retainer.
2. Description of the Related Art
In a press die set in which upper and lower dies are vertically slidden, relative to each other, through the intermediary of guide posts, a retainer and guide bushes so as to perform a punching process.
Conventionally, a ball retainer shown in FIG. 23 has been widely used as the above-mentioned retainer. The ball retainer has a substantially cylindrical shape plastic casing 601 in which several ball bearings 602 are rotatably held. Since the thickness of the casing 601 is less than the diameter of the ball bearings 602, the ball bearings pierce through the inside of the casing so as to make contact with a guide post while the casing does not make contact with the guide post. Similarly, the ball bearings make contact with a guide bushing which surrounds the exterior of the ball retainer. Further, when the ball bearings are rotated, the guide post, the ball retainer and the guide bushing are slidden, relative to each other.
The conventional guide post is columnar, having an outer diameter slightly smaller than the inner diameter of the retainer. Further, the conventional guide bushing is cylindrical, having an inner diameter slightly larger than the outer diameter of the retainer. Gaps between the ball bearings, the guide post and the guide bushing, are filled with lubricant such as grease so as to enable smooth slide motion.
However, since the conventional retainer uses ball bearings, and accordingly they make point-contact with the guide post and the guide bushing, the total contact area is not so large even though a larger number of ball bearings are used. Accordingly, a high pressure is exerted to the ball bearings, causing several problems such as occurrence of thread-like scratches on the guide post, breakage of a lubricant film, occurrence of friction heat, and further, in the worst case, occurrence of seizure.
Further, the individual bearings are made into point contacts with the guide post and the guide bushing, excessive play or rattling occurs, deteriorating the dimensional accuracy thereof and further the freedom thereof is very much so the positional adjustment therefore is difficult.
Further since the conventional retainer has a large frictional resistance, it inevitably requires a large force for slide motion of the die set. Further, the ball bearings are lined in an oblique direction, and accordingly, the relative motion between the guide post and the retainer is likely to effect in this oblique direction. The same is said to the relative motion between the retainer and the guide bushing. As a result, the motion of the die set is not in a true vertical direction but is added thereto with rotational motion, causing spiral motion or precession, and accordingly, an unpreferable lateral load is exerted to a punching cutter in dies, thereby possibly causing problems of breakage and abrasion.
The present invention is devised in order to solve the above-mentioned problems, and accordingly, one object of the present invention is to provide a novel press die set having high dimensional accuracy, which hardly fails during operation, and which facilitates the positional adjustment.